Firstly, Daumueller, as has been pointed out Channel 9 is available outside of US airspace. My United flight from ORD
772 2 weeks back had it on from boarding till I left my seat, and I was 42A!!!
Secondly, Ual777contrail, not entirely sure why my flight didn't have Channel 9 on. I'm guessing it is because the 744 I was on was one of the older aircrafts in the fleet. No PTV's and the Screen at the front seemed to be black and white.
We also have to remember its totally up to the Capt. whether or not they have it turned on or not.
Aircraft wise, i've been on a United 763, 733, A320, 752 and 772 and they all had channel 9 on. To be honest, not sure why the Capt would choose not to have it on. It's one of the most innovative things out there in the aviation world!!